Orofacial muscle pain is much more prevalent and severe in women compared to men. Sex differences also play an important role in individuals' responses to treatment. However, with etiology, pathophysiology and sex-related mechanisms not fully understood, current treatments for orofacial muscle pain conditions are largely inadequate. Peripheral uses of cannabinoids have emerged as attractive alternatives or adjuncts to treatment with opioids, due to the centrally related side effects associated with opioids treatments. Peripheral administration of cannabinoids produces sex-dependent analgesic responses under inflammatory conditions and is likely due to the differential CB1 expression in trigeminal ganglia (TG). Inflammatory cytokines have been shown to modulate both opioid and cannabinoid receptor expression. This study proposes to investigate whether inflammatory cytokines induce greater up-regulation of CB1 in TG in males than females, and whether estradiol is involved in the sex differences in the induction of CB1 by cytokines. Real-time RT-PCR and western blot experiments will test (1) whether inflammatory cytokines induce a greater up-regulation of CB1 expression in males than females by applying cytokines in TG primary cultures and (2) whether inflammatory cytokines induce a greater up-regulation of CB1 expression in males than females by directly injecting cytokines into the masseter muscle in intact animals. This study will lead to better understanding of the mechanisms underlying sex differences in the regulation of CB1 expression under inflammatory conditions and sex differences in peripheral cannabinoid receptor-mediated analgesia. PUBLIC HEALTH RELEVANCE: Orofacial muscle pain related to temporomandibular disorders affects approximately 10-12% of the population, with a higher prevalence in women than in men. With etiology, pathophysiology and sex-related mechanisms not fully understood, current treatments for these pain conditions are still inadequate. In accordance with the missions of the NIDCR and the FOA: PA-10-107 this study proposes to investigate whether inflammatory cytokines induce sex-dependent CB1 expression in TG and whether estradiol modulates this induction. Understanding the mechanisms underlying sex differences in peripheral cannabinoid-mediated analgesia will enable the development of sex-based and mechanism-based therapeutic interventions for the treatment of inflammatory orofacial muscle pain. This proposal will serve as a platform on which I can develop into a clinician/scientist.